NO! That's not correct.
Roberts had to rewrite the statute to call it a tax before allowing it.
He agreed with the oral arguments of the DOJ who, being very concerned that the Commerce Clause argument would be declared unconstitutional, emphatically stated to the court that the "mandate penalty" was a tax and therefore constitutional.
Nowhere in the bill itself was this mandate called anything but a penalty. The DOJ defined it as a tax.
The Government asked the Court to view the mandate as imposing a tax on those who do not buy that product.
http://www.supremecourt.gov/opinions/11pdf/11-393c3a2.pdf